Origins and Processes of Salinization of a Plio-Quaternary Coastal Mediterranean Multilayer Aquifer: The Roussillon Basin Case Study

Salinization of coastal aquifers represents a threat to groundwater resources, especially in Mediterranean regions. We report geochemical and isotopic vertical variability in the Quaternary and Pliocene aquifer of the Roussillon Basin (S France). Aquifers layers are not equally impacted by salinization, with EC ranging from 459 to 43000 μS.cm−1. Groundwater chemical compositions highlight cation exchange processes, in addition to a simple binary mixing between fresh groundwater and seawater. The multi-isotope approach consisting of complementary tracers allows evidencing water-rock interaction processes, such as dissolution or adsorption onto clay matrices.